This invention relates generally to the art of film wrapping systems for use in wrapping objects with shrink wrap film, such as polyurethane wrapping film, and more particularly to improvements directed to dispensing such film from a film roll.
A wide variety of systems are known for wrapping packages in thermoplastic film. Some of these machines are known as L-sealers because they form “trim seals” utilizing a web of center folded film. More recent machines have utilized a continuous longitudinal sealer and a cross sealer which moves at approximately the velocity of the packages as they travel through the machine so that it is not necessary to stop the packages while performing the end sealing operation. Such prior art machines have generally been of three types. One type had a continuous side sealer and a complex series of multiple flighted end sealing jaws which were spaced for a particular product. This type required substantial set-up time for change in length of product to be wrapped. A second machine of this type, while making packages similar to those produced on an L-sealer worked by drawing film off a roll under tension, folding it around the product, drawing it past a hot knife side sealing mechanism and then formed the end seal with a moving end sealer.
A third type of machine had an overlapped longitudinal seal on the top or bottom of the wrapped packages. Since the overlap not only ran along the bottom of the packages but also ran halfway up both ends, the packages lacked the neat appearance and hence the sales appeal of the trim sealed packages as made on the L-sealers. Since many of the products so wrapped are sold in self-service retail stores, the appearance of the package has an important effect on the sales of the product. An additional disadvantage of the overlapped seal is that the width of the web of film must be precisely correct, requiring an exact width film for each size of product.
Shrink wrap packaging systems of these types process and wrap a variety of different products. Commonly, such products are of differing shapes, sizes and dimensions. For example, shrink wrap packaging systems may process and wrap a single compact disc (CD) package which is very thin or other consumer retail items which have a significantly greater height and larger vertical dimension.
One problem associated with most known shrink wrap packaging system is the difficulty to efficiently process and wrap a wide variety of packages and products, especially those having distinctly different dimensions and heights. For example, most known shrink wrap packaging systems utilize film which is provided on a roll in two plies with each ply being joined together by a longitudinal fold line. The two-ply film is dispensed from the supply roll typically in a direction generally perpendicular to the feed direction of the products to be wrapped. As the film is dispensed and delivered to a wrapping station of the shrink wrap packaging system, it is commonly inverted and reoriented to provide an opening for convenient access and entry of the products between the dual plies of the film. The film is reoriented by an upper and a lower film inverting rod or plow system. The upper and lower film inverting rods are positioned above and below, respectively, the feed conveyor which is advancing the products to be wrapped. Examples of such an arrangement are shown in U.S. Pat. Nos. 3,583,888; 3,583,889; 4,035,983; and 4,219,988, each of which are incorporated by reference herein.
The film inverter rods disclosed in the above-identified patents are each fixed relative to one another so that the spacing between the inverter rods is fixed. Recent advancements in the art of shrink wrap packaging systems have included adjustable film inverter rods to accommodate a variety of differing height products being wrapped. As such, the spacing between the film inverter rods may be adjustable.
However, one problem associated with adjustable film inverter rods is that the delivery of the two-ply film to the film inverter rods is often misaligned providing for poor geometry for the film being delivered to the film inverter rods once the spacing between the inverter rods is changed. Optimally the free edges of the upper and lower plies should be generally aligned with one another downstream from the film inverter rods for proper wrapping of the products and positioning of the side seam on the product. However, when the upper film inverter rod is moved relative to the lower film inverter rod for a different height product, the geometry of the film being delivered and processed at the wrapping station becomes misaligned. As a result, the film will not track properly and will not be in the required tubular configuration at the wrapping station. This requires readjustment and/or refeeding of the film through the various rollers, significant operator involvement and down time of the packaging system. The misalignment of the upper and lower plies of the film results in improperly wrapped products, side seals on the products which are located in a conspicuous or improper location, inefficient use or waste of the film wrapping material and other associated problems.
Therefore, a need exists in the shrink wrap packaging industry for a packaging system which can readily accommodate a wide variety of product configurations and heights without the above-described problems associated with known film delivery systems and wrapping operations.